"S" Curves ?

[Don Gibson]

 I'll try to simplify - and not make an 'S' of myself, doing it.

1. MOST American RR cars wheels ride on INBOARD pivot points. Car ends extend beyond. This is what causes the problem. The car ends stick out on our toylike curves. 22 inch radius is not what REAL RR's use.

2. SINCE MOST RR cars are pulled by CENTER mounted couplers. Trouble starts when encountering sharp curves, and 'S' curves, are doubly sharp.

3. When COUPLERS have trouble handling these excessive swings (Different geometry), they sometimes try to pull cars off the track.

MANUFACTURERS of 'toy' RR cars use the the dreaded 'Talgo' (truck mounted) couplers to compensate - "dreaded", because REAL railroads don't use them, and we're 'modelers' - after all - plus they are undependable when backing up (pull, don't push). 

American 'style' turnouts (#4, #6, etc.) all have a couple of inches of straight, to help alleviate this problem, so they form superior 'ladders' and 'crossovers'. The theory is: by adding some 'straight' you take the 'S' out of it.

IF ONE is a beginner, 'curve-based' turnouts such as Atlas' 'Snap track' will derail more cars than their #4, and the higher numbers are better yet. "But I run out of board!" ...

Decisions, decisions. Welcome to the club.

[BRAKIE]

Bill,A "S" curve can be made with 22" curves if short 40 and 50 foot cars are used.I recommend nothing less then a 24" "S" curve with a straight section exceeding 2 locomotive or long car lengths if possible.

[Bill54]

I appreciate everyone's input. 

I started this thread before looking in the Layouts fourm where they started the same thread.  Thanks Tom for pointing that out. 

So if I understand correctly, "S" curves can be used depending on the length of the cars and locos that are being used and the radius of the "S" curve in question.  "S" curves with an 18" radius would not be acceptable where 30" or greater I shouldn't have a problem.  Still if at all possible a straight section at least as long as the longest car/loco should be between the opposing curves.

Thanks again for everyone's input.

Bill

 

 

[tstage]

Bill,

I included this in another thread over on the Layout forum.  This is why it's important to have them on your mainline.

Tom

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S-curves are also a problem with longer locomotives - e.g. 6-axles.  I had a friend come over one time to test out his new Overland SD-40 or AC6000 on my layout.  (Can't remember which.  All I remember was that it was loooooooooooonng.) 

On my mainline, I have a section that has opposing curves, separated by a 9" piece of straight track.  Since the span between the locomotive's truck was longer than the 9" straight track, there's a brief moment where the locomotive's front truck is rotating CW and the back truck is rotating CCW.  This caused one of the trucks to raise up slightly then come back down with an audible "clunk".

As mentioned previouisly, whenever possible it's best to have a section of straight track separating opposing curves that is as long or longer than your longest locomotive or car. 

Tom

[BRAKIE]

Bill,There are times when a "S" curve is needed perhaps to get around a fixed object like a support coulmn or perhaps and more then likey the "S" curve was designed into the track plan after all there is nothing like a train snaking through a sweeping "S" curve.

Even a small  "S" curve in a yard isn't a bad thing because we usually switch cars at slow speeds..If we use a #4 and above switch as crossovers there is no real need for a straight section between switches because there is no "S" curve due to the short straight section on the leg of the switches..

[DougF]

Bill: 

 

You can have S curves. 

 

If you do not have a straight section between the two curves then you will have more trouble with derailments from coupler strain. 

 

If you put a length of straight the length of your longest car between the two curves you will eliminate the coupler strain.  The longer the straight the less the strain.  Adding easments on the curves will also help.

 

A commonly missed S curve is the one between switches on a double cross over and in yard trackage ladders.

 

Hope this helps.

 

Doug

[MisterBeasley]

The problem comes from long cars and normal body-mounted couplers.  When a pair of cars goes around a curve, the couplers have to swing to one side to stay connected.  On a regular curve, both couplers swing to the same side.  On an S-curve, though, the couplers must swing in opposite directions, and this sometimes pushes them beyond their limits, and the cars are pushed sideways enough that they derail.

[Bill54]

I noticed when asking to critique layout designs "S" curves are fround upon and pointed out with a suggestion to insert a straight section between the two opposing curves.

I'm new to model railroading (1 1/2 years).  I am designing my first HO layout and wondering if there is a reason one should not have an "S" curve on a layout.

Will someone please explain?

Thanks,

Bill